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Records of the Australian Museum (2009) Vol. 61 
selected as the outgroup, as this genus has been considered 
to be the sistergroup of Megalomma in previous phylogenetic 
analyses (Fitzhugh, 1989, 2003; Fitzhugh & Rouse, 1999). 
Characters and states. The characters and their states 
used for analysis were those considered as diagnostic in 
traditional taxonomic studies (Perkins, 1984; Knight- 
Jones, 1997; Fitzhugh, 2002, 2003; Giangrande et al., 
2007; Giangrande & Licciano, 2008; Tovar-Hernandez & 
Salazar-Vallejo, 2008), as well as others observed to vary 
within Megalomma species by us and other workers (Tovar- 
Hernandez & Salazar-Vallejo, 2008; Fitzhugh, 2003; pers. 
obs.). Absence/presence and multistate coding methods 
were used; multistate characters were equally weighted and 
unordered. Missing data were scored with “?”, inapplicable 
data with a hyphen. The score given for each state implies 
nothing about polarity or order. 
The material studied for the present study included the 
whole range of variability of development of the dorsal collar 
margins described so far in Megalomma. Megalomma sp. 2 
displays collar margins that are separated by a wide gap and 
therefore has no dorsolateral pockets (which are pouch-like 
structures formed by the collar and peristomium) (Fig. 1A); 
Megalomma interrupta n.sp. has collar margins that are not 
fused to the faecal groove but low pockets are present (Fig. 
IB); Megalomma phyllisae n.sp. has collar margins fused 
to the faecal groove, pockets present and low dorsal lappets 
(Fig. 1C); and M. cf. acrophthalmos has dorsal lappets that 
are well developed and spatulate-shaped (Fig. ID). 
In specimens that display only shallow membranous 
dorsal collar margins that extend all the way to the faecal 
groove (and also form shallow pockets dorsolaterally), the 
interpretation of these structures was based on whether we 
could insert forceps under the margin and the tip was hidden 
by the margin, indicating that there was a membranous 
extension of the collar across to the faecal groove (Fig. IB), 
or not (Fig. 1 A). Where dorsal lappets are present, this is not 
ambiguous, as these are extensions of the collar and hence the 
collar is obviously fused with the faecal groove (Fig. 1C,D). 
After examination of several species of Megalomma, we 
have observed two general forms of inferior thoracic chaetae. 
They all match the category of “broadly hooded” chaetae 
as figured by Perkins (1984) and Fitzhugh (1989), and also 
referred to as “subspatulate” by other workers. They have a 
short distal hood, gently curved margins and a fine, elongate 
tip (Fitzhugh, 1989). Under light microscopy the hood can 
be distinguished on both sides of the shaft as symmetrical 
wings (different to a narrowly hooded chaetae where the 
hood is only visible on one side) and the shaft almost reaches 
to the tip of the chaetal hood (different to “paleate” chaetae 
which have short emergent shafts). The Megalomma species 
described in this paper display two kinds of “broadly hooded” 
inferior thoracic chaetae: those with the distal end narrowing 
abruptly and which are referred to from now on in the text 
as type A (Fig. IE), and those with a progressively tapering 
distal tip, referred in the text as type B (Fig. IF). 
Analytical methods. A matrix including 20 terminal taxa 
and 14 characters was constructed in NDE, Nexus Data 
Editor (Page, 1998). The parsimony analysis was performed 
using NONA 2.0 (Goloboff, 1993). Tree searches were 
complete using the heuristic search, with the multiple tree 
bisection and reconnection (TBR + TBR) strategy, selecting 
25000 replicates and holding 5000 trees at each step and 
starting 5 trees per replicate. Cladogram topologies and 
character-state optimization were examined using Winclada 
(Nixon, 2002), showing only unambiguous changes. Nodal 
supports were determined calculating jacknife proportions 
from 1000 replicates using TRB, in Winclada. Tree metrics 
are abbreviated as follows: tree length (TL), consistency 
index (Cl), and retention index (RI). 
List of characters and states used: 
1 Subdistal sessile compound eyes: (0) absent; (1) 
present. 
2 Arrangement of subdistal eyes: (0) in dorsalmost pair 
radioles (one to 3 pairs); (1) in all radioles; (2) in 
most radioles; (3) in dorsal most and lateral. 
3 Rows of cells in radiolar skeleton: (0) four; (1) eight 
to ten; (2) more than 10. 
4 “Caruncle”: (0) absent; (1) present 
5 Ventral sacs: (0) absent; (1) present. 
6 Dorsal collar margins: (0) fused to faecal groove; (1) 
not fused to the faecal groove. 
7 Dorsal collar pockets: (0) absent; (1) present. 
8 Dorsal collar lappets: (0) absent; (1) present. 
9 Thoracic ventral shields: (0) separated from tori; (1) 
only shields in anterior segments in contact with 
tori; (2) all ventral shields in contact with tori. 
10 “Interramal eyespots”: (0) absent; (1) present. 
11 Inferior thoracic chaetae: (0) with the distal end 
narrowing abruptly (type A); (1) or with a 
progressively tapering distal tip (type B). 
12 Handle of thoracic uncini: (0) shorter than length 
of distance of main fang to breast; (1) 1-2 times 
length of distance form main fang to breast; (2) >2 
times length of distance form main fang to breast. 
13 Companion chaetae: (0) with distal end inflated, 
dentate and with a tapering membrane (1) with an 
asymmetrical, teardrop-shaped membranous hood 
14 Abdominal chaetae: (0) narrowly hooded; (1) 
elongate, broadly hooded. 
The matrix of species, characters and states is presented 
in Table 3. 
Taxonomic account 
Megalomma Johansson, 1925 
Type species. Branchiomma kollikeri Claparede, 1869, a 
junior synonym of Amphitrite vesiculosum Montagu, 1815 
(see Tovar-Hernandez & Salazar-Vallejo, 2008). 
Synapomorphy. Presence of subdistal, sessile and 
compound radiolar eyes, at least on the internal margin of 
the dorsalmost pair of radioles (Fitzhugh, 1989). 
Remarks. There are other morphological characters that 
have been included in the diagnosis of the genus (see last 
emendation by Tovar-Hernandez & Salazar-Vallejo, 2008) 
and are herein assessed. 
Megalomma has been attributed with rounded external 
margins of radioles, but some of the species described in the 
present study clearly show distinct externally quadrangular 
